8252

• UCREFRP Catalog Number: 8252
• Author: Allred, T. M. and J. C. Schmidt.
• Title: Channel Narrowing of the Green River Near Green River, Utah
• USFW Year: 1999.
• USFW - Doc Type: History, Rates, and Processes of Narrowing.
• Copyright Material: NO

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periods of time. The post-dam variability in effective discharge appears to be

greater than the pre-dam condition.

The reco~d of channel width change at the cableways provides a rare

continuous record to compare with estimates, of effective discharge (Fig. 17).

Effective discharges were greater than 1400 m3/s prior to 1920 and steadily

decreased to about 680 m3/s by the mid-1930s. Following closure of Flaming

Gorge Dam, effective discharges dropped to approximately 600 m3/s, but large

floods between 1983 and 1986 increased effective discharges to magnitudes

that had not occurred since 1930.

There is generally good agreement between the trend in effective

discharge and the trend in channel width (Fig. 17). The time phase of the

. 1930s narrowing coincides with a substantial decrease in effective discharge.

However, the large increase in effective discharge during the floods of the mid-

1980s had no effect on channel width. These large floods simply elevated the

existing floodplain surface (Fig. 16). These data suggest that narrowing can

begin soon after effective discharge is reduced, but even large increases in'

,

effective discharge do not necessarily lead to channel widening. Dense

riparian vege.tation that often forms near channel margins, in this case

saltcedar, may be sufficient to stabilize banks and prevent widening of the

channel except in the largest long-duration floods.

Andrews (1980) found that bankfull discharges identified in the field were

well correlated with effective discharges for streams in the Vampa River basin.